The invention relates to a single lens reflex camera with electrical shutter, and more particularly, to a supply voltage alarm unit including an electromagnet assembly for producing an alarm to indicate that a supply voltage is insufficient to operate an electrical shutter as well as a self-timer which delays the operation of the electromagnet assembly.
A single lens reflex camera incorporating an electrical shutter must be provided with some means which indicates to a user the fact that a supply voltage is insufficient to operate the electrical shutter or that the loading of a supply battery has been inadvertently forgotten. Otherwise, the user fails to take the picture which he intended by depressing a shutter button. To accommodate for this difficulty, there has been proposed an arrangement in which the depression of a shutter button is inhibited whenever the supply voltage is insufficient, the supply battery is not loaded or a power switch is left open. However, the means which is proposed at this end also prohibits the depression of the shutter button whenever the exposure provided by the electrical shutter falls outside a range of proper exposure or prior to or during the film winding. This fails to provide the user with an indication of a specific cause for which the depression of the shutter button is inhibited.
There is another arrangement in which a lamp is illuminated in the course of depressing the shutter button whenever the supply voltage is above a given level. However, it should be noted that in the process of taking a picture, the user is almost entirely absorbed in the photographing operation, and as a matter of fact, users scarcely recognize the illumination of such lamp.
A further proposal relates to a camera incorporating a shutter locking mechanism which becomes effective when the supply voltage is found to be insufficient. However, the mechanism is complex, and maintains the shutter locked if the supply voltage is returned to a normal level. This requires a separate release mechanism, contributing to a further complication and an increased cost of the resulting arrangement.